Wireless universal serial bus (USB) is a technical standard obtained by extending USB widely spread as a wire communication standard for a short-range communication so that usability of wireless communication is achieved while security and high speed processing of a wire communication are ensured, and a specification of the wireless USB is formulated by the Wireless USB Promoter Group that is a lower organization of the USB Implementers Forum (USB-IF).
The wireless USB employs ultra-wideband (UWB) technology as a wireless technology. The UWB is a wireless communication system using a broad frequency bandwidth of 7.5 gigahertz (GHz) from 3.1 GHz to 10.6 GHz. Physical layers of the UWB have been standardized by the Institute of Electrical and Electronics Engineers (IEEE) that formulates standards according to the IEEE 802.15.3a.
Two modulation systems, i.e., a Direct Spread-UWB (DS-UWB) system and a Multiband-Orthogonal Frequency Division Multiplexing (MB-OFDM) system, are used for the physical layers of the UWB.
In the DS-UWB system, two bands (dual band), i.e., a low band from 3.1 GHz to 4.9 GHz and a high band from 6.2 GHz to 9.7 GHz are used. A signal is transmitted after Quadrature Phase Shift Keying (QPSK) or Binary Phase Shift Keying (BPSK) is performed as primary modulation and Code Division Multiple Access (CDMA) is performed as secondary modulation. Furthermore, the DS-UWB system employs Direct Sequence Spread Spectrum to transmit a signal.
In the MB-OFDM system, a bandwidth from 3.1 GHz to 10.6 GHz is divided into 14 bands (frequency bands). A signal is transmitted after the QPSK is performed on each of the bands as primary modulation to carry a digital signal on a radio wave and OFDM modulation is performed as secondary modulation to achieve communication that can tolerate interference with a different radio wave. WiMedia PHY is formulated by the WiMedia Alliance as a standard for a physical (PHY) layer using the MB-OFDM.
A transmission power level is controlled in the UWB by using the above modulation systems. Specifically, the Federal Communications Commission (FCC) defines that an equivalent isotropically radiated power (EIRP) indicating a regulation value of the transmission power level per 1 megahertz (MHz) in the UWB is set to less than −41.25 dBm. It can be converted into about 0.5 milliwatt (mW) in terms of total electric power, and it is about one twentieth of total electric power of a Personal Handy-phone System (PHS).
WiMedia MAC is formulated by the WiMedia Alliance as a protocol for a Media Access Control (MAC) layer. Thus, the wireless USB conforms to a USB technology based on the USB Specification Revision 2.0 formulated by the USB-IF in addition to a wireless technology such as the WiMedia PHY and the WiMedia MAC. Therefore, if the wireless USB performs communication within a range of less than three meters, the wireless USB can transmit data at 480 megabits per second (Mbps) that is a maximum data transfer rate according to the USB Specification Revision 2.0.
Because the wireless USB has low transmission power that is a characteristic of the UWB, it is considered that the wireless USB is used in a Personal Area Network (PAN) in which it is assumed that a radio wave range is less than 10 meters. Therefore, it is possible to provide a communication technology with less risk of eavesdropping that often occurs in a wireless local area network (LAN) and with high security.
As described above, compared with the wireless LAN, the wireless USB has characteristics of higher speed processing and higher security, and therefore the wireless USB has attracted attentions as a next-generation wireless technology to be used at an office.
However, a communication type of the wireless USB is a hub-and-spoke type including a wireless USB host playing a central part and up to 127 wireless USB devices to be controlled by the wireless USB host. Specifically, each of the wireless USB devices is controlled by one wireless USB host.
Therefore, if the wireless USB technology is used without modification, a plurality of personal computers (PCs) serving as the wireless USB hosts cannot share one printer serving as the wireless USB device.
For example, Japanese Patent Application Laid-open No. 2007-306057 discloses a technology in which if the wireless USB device performs communication with a wireless USB host when a different wireless USB host reserves a medium access slot (MAS) for transmitting data on the WiMedia MAC, the wireless USB device switches the wireless USB host with which the wireless USB device 5 performs communication.
Japanese Patent Application Laid-open No. 2007-293708 discloses a technology in which a wireless USB device includes the same number of controllers and buffers called end-points as that of connectable wireless USB hosts, so that the number of the wireless USB hosts that can perform communication with one wireless USB device is physically increased.
The Wireless USB Specification Revision 1.0 created by the Wireless USB Promoter Group defines that a wireless USB host periodically continues to transmit a Micro-scheduled Management Command (MMC) packet that is a control packet.
The MMC packet can contain a connection host identifier (CHID) in 16 bytes that is identification information for identifying the wireless USB host, information about time when the wireless USB host transmits data to a wireless USB device, information about time when the wireless USB device transmits data to the wireless USB host, device control information, and the like, as an information element.
The USB Specification Revision 2.0 defines that a USB device includes at least one configuration descriptor. If the wireless USB device includes a plurality of configuration descriptors, a wireless USB host determines which configuration is to be applied to the wireless USB device.
Therefore, in the technology disclosed in Japanese Patent Application Laid-open No. 2007-306057, there is no guarantee that each of the wireless USB hosts desires the same configuration to be applied to the wireless USB device, and as a result, there can be mismatch of the configuration, i.e., the configuration applied to the wireless USB device is not a desired one for a wireless USB host.
Furthermore, in the technology disclosed in Japanese Patent Application Laid-open No. 2007-293708, because the wireless USB device needs to include the same number of the controllers and the end-points as that of the wireless USB hosts, a circuit size is increased.
The present invention is made to solve the above problems, and has an object to provide a wireless USB device and a wireless USB communication system that can prevent mismatch of the configuration with respect to each of the wireless USB hosts without increasing a circuit size in the wireless USB device.